KR960003817B1 - Process for cold forming propylene copolymers - Google Patents

Abstract

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Description

Process for Plastic Processing of Propylene Copolymer

The present invention relates to a method of cold forming a propylene copolymer.

Cold forming or solid phase forming is generally used to produce finished products from sheets or other manufactured preforms below the melting point of the preform. A common example is the stamping of steel sheets to manufacture automotive body parts. The same method is commonly used to process polymers such as polypropylene and / or impact resistant polypropylene copolymers.

The main problem associated with plasticizing or molding a polymer is that over time, the molded part tends to return to its original shape, especially when exposed to elevated temperatures. This is obviously undesirable because the geometry of the desired part is changed. Two other problems associated with plastic processing of polymers are: (i) uneven deformation resulting in changes in wall thickness during processing, in severe cases tearing of preforms, and (ii) weak definition of small parts of the machined part. )to be.

These problems can be alleviated by processing at elevated temperatures closest to the melting point in the range below the melting point of the polymer. However, at such high temperatures it is often difficult to handle the polymer. In the case of sheets, sagging or deformation is a problem because of its weight. A further disadvantage is that at higher temperatures accurate temperature control is required. In addition, when high temperatures are used, the process cycle is longer. Therefore, it is desirable to process the polymer at temperatures well below the melting point.

Accordingly, it is an object of the present invention to provide a method of processing an impact resistant polypropylene copolymer at a temperature below its melting point, thereby providing a product having excellent sharpness, which is dimensionally stable and homogeneously processed. Other objects and advantages will be apparent below.

According to the present invention, the object is that a) about 10% by weight (based on total composition) of ethylene to at least one other alpha-olefin interpolymer having a crystallinity of at least about 20% b) a propylene homopolymer or propylene to at least one The impact-resistant copolymer composition incorporated in the matrix, which is an interpolymer with other alpha-olefins, is plastically processed at a temperature above the melting point of the ethylene interpolymer, below the homopolymer of propylene or the melting point of the interpolymer. Satisfied by the method of manufacture.

In applications requiring high levels of low temperature impact strength, "impact resistant polypropylene copolymers" are used. These polypropylene copolymers are generally incorporated into a homopolymer matrix by mixing an elastomeric impact modifier (such as ethylene / propylene copolymer rubber material (EPR)) with the homopolymer with EPR or by preparing the copolymer in situ. It is prepared by incorporation.

Conventional methods for producing impact resistant polypropylene copolymers are preferably selected from (a) an amount of propylene or propylene sufficient to provide a copolymer having about 5% by weight or less (based on the weight of the copolymer) of the other alpha-olefin. Selectivity different from catalyst precursors, hydrocarbylaluminum promoters and electron donors containing titanium, magnesium, chlorine and electron donors in a first reactor under hydrogenation conditions with at least one other alpha-olefin having 2 or 4 to 8 carbon atoms and polymerization conditions Contacting with a catalyst comprising a modifier to obtain a propylene homopolymer or a mixture of propylene with an alpha-olefin and a mixture of an active catalyst, (b) transferring the mixture of step (a) to a second reactor, and (c (Iii) to provide an ethylene / alpha-olefin copolymer having an ethylene content of at least about 85% by weight based on the weight of the copolymer. Preferably the sufficient amount of ethylene is the other alpha-carbon atoms of 3 to 8 and a step of applying the at least one olefin and hydrogen to the second reactor.

The steps of the process and the conditions and catalysts used in each reactor may be as described in US Pat. No. 4,414,132 or US Patent No. 051,853 (filed May 19, 1987) and the reactor is US Pat. No. 4,482,687 Gas phase reactors such as the fluidized bed reactor described in the arc.

The atomic ratio or molar ratio of the catalyst component is generally as follows.

The polymerization can be carried out using a gas phase, slurry or solution method; However, the polymerization in the second reactor is preferably carried out in the gas phase. For gas phase polymerization, a fluidized bed reactor is preferably chosen as the reactor. U.S. Patent No. 4,482,687 mentions a fluid bed reactor.

In general, the fluidized bed reactor is operated at a temperature of about 40 to about 150 ° C, preferably about 60 to about 120 ° C and a pressure of about 50 to about 700 psig, preferably about 250 to about 550 psig. The flow gas velocity is about 0.1 to 3.0 feet per second, preferably about 0.5 to about 2.0 feet per second. The weight flow rate ratio of monomers to catalyst in the first reactor is from about 1000: 1 to about 100,000: 1, preferably from about 10,000: 1 to about 100,000: 1.

As mentioned above, propylene or a mixture of propylene and one or more other alpha-olefins is introduced into the first reactor together with hydrogen and a catalyst. Examples of alpha-olefin components may be ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene or 1-octene, or may be various mixtures of alpha-olefins. The molar ratio of alpha-olefin to propylene is about 0.01: about 0.06, preferably about 0.015: about 0.04. The molar ratio of hydrogen to propylene alone or to a mixture of propylene and alpha-olefin is about 0.001: about 0.45, preferably about 0.004: about 0.1. In the case of propylene and alpha-olefins, an amount of balls sufficient to provide a copolymer having up to about 5% by weight of alpha-olefin, preferably from about 0.1 to about 2% by weight, based on the weight of the copolymer. Monomers are used.

A homopolymer or copolymer mixture of propylene incorporated into the polymer matrix with an active catalyst under the mixing and conditions of the abovementioned components is obtained. These mixtures are moved from the first reactor to the second reactor and it is preferred to add only a promoter to the second reactor, but additional catalysts, promoters and selectivity modifiers may be added. For some catalysts, none of these three components are added.

In the second reactor, ethylene and alpha-olefins, generally propylene, can be introduced at a molar ratio of about 10 to about 100 moles of ethylene per mole of alpha-olefins (ie, all alpha-olefins except ethylene). Preferred proportions range from about 10 to about 50 moles of ethylene per mole of alpha-olefin. Ethylene copolymers containing at least about 85% ethylene, preferably about 90 to about 99% ethylene, and a crystallinity of about 20 to about 60%, preferably about 35 to about 50%, based on the weight of the copolymer The purpose is to provide. The percent crystallinity attributable to the copolymer fraction can be calculated from the weight fraction of the second reactor product and can be a measure of the heat of fusion required to melt the copolymer fraction by differential scanning calorimetry (DSC). An amount of ethylene / alpha-olefin mixture is sufficient to provide about 10 to about 50 weight percent copolymer fraction, most preferably about 20 to about 35 weight percent copolymer fraction, based on the weight of the product. It is preferable to add. Hydrogen, together with ethylene and alpha-olefins, is also introduced into the second reactor. The molar ratio of hydrogen to the mixture of ethylene and alpha-olefin is about 0.1 to about 1.0, preferably about 0.1 to about 0.4. It should be noted that all or some of the alpha-olefins in the second reactor can be introduced from the first reactor. Both reactors are operated continuously. The product is an ethylene / alpha-olefin copolymer incorporated in a matrix of propylene homopolymer or copolymer.

When the alpha-olefin comonomer is introduced into the first reactor, the stiffness (flexural modulus) of the final product is somewhat lower but the Izod impact strength is somewhat improved.

Impact resistant polypropylene copolymer products can be processed into suitable preforms by well known polymer processing methods including injection molding, extrusion and pressure molding. The preform material has certain suitable geometry required by the finished part. As an example, a cup or a tray can be produced from the sheet material produced by the extrusion method. Polymer processing methods are well known and described in the literature. Injection molding, extrusion and pressure molding methods are summarized in the literature (Modern Plastics Encyclopedia-1988: pages 226-250, McGraw-Hill (1987)).

The process comprises (a) (i) a crystallinity incorporated in the matrix with a matrix which is (a) a propylene homopolymer or a copolymer of propylene with at least about 5% by weight of one or more other alpha-olefins (based on the weight of the copolymer). A impact resistant polypropylene copolymer comprising at least about 10% by weight (based on the weight of the impact copolymer) of ethylene and at least one other alpha-olefin, of at least 20%, and (b) impact resistant polypropylene The copolymer may be described as a process for plasticizing the impact resistant polypropylene copolymer, characterized in that the copolymer is calcined at a temperature not less than the melting point of component (ii) or less than the melting point of component (iii).

The term “baking” is a general meaning including processes that are well known and used, in which polymer modification and processing into finished parts are carried out below the melting point of the polymer. These methods include solid state forging, pressing, roll forming, and coining.

General molding temperatures and methods of various thermoplastics are described in the SPE publication (October 1969, Volume 25, pages 46 to 52).

The calcining is carried out at a temperature above the melting point of the ethylene / alpha-olefin copolymer produced in the second reactor, i.e. below the melting point of the propylene homopolymer or propylene copolymer produced in the first reactor. Typical low temperatures are about 130 to about 135 ° C and typical high temperatures are about 145 to about 155 ° C.

Patents, patent applications, and other publications mentioned herein are incorporated herein by reference.

The invention is illustrated by the following examples.

[Examples 1-3]

ASTM Type I tensile test bars are prepared from the following polymers:

Example 1. Propylene Homopolymers.

Example 2. Conventional impact resistant polypropylene copolymer.

Example 3. Impact resistant polypropylene copolymer for the present invention.

In Examples 2 and 3, the matrix is a homopolymer of propylene and the copolymer incorporated into the matrix is an ethylene / propylene copolymer. Conventional methods for preparing impact resistant copolymers are described above.

Tensile test bars are prepared by injection molding polypropylene at a melting temperature of 440 to 460F. The bar is 8 inches long, 1/8 inches thick and has a maximum width of 3/4 inches. The bars are heated in a circulating air oven at 140 ° C. and then the molding operation is simulated by hand wrapping around a 1.5 inch steel mandrel.

After age hardening for 1 day, the diameter (inside) of a coil is measured. The polymers of Examples 1 and 2 differ significantly from the molding dimensions. The polymer of Example 3 is almost identical to the original molded structure, which demonstrates the excellent dimensional stability of the polymer thus formed.

The variables and results are shown in the table below.

TABLE 1

Footnotes in the table:

1. Melt flow rate is measured under ASTM D1238, Condition L, at 230 ° C. and 2.16 kg load. The results are given in decigrams per minute (dg).

2. The secant flexural modulus is measured by ASTM D790, Method A. The result is given in pounds per square inch (1b).

3. The tensile yield strength is measured at ASTM D638: elongation rate 2in / min. The results are given in pounds per square inch.

4. Copolymer fraction is the percentage of ethylene / propylene copolymer incorporated into the matrix based on the total weight of copolymer and matrix.

5. Ethylene in the copolymer fraction is the percentage of ethylene / propylene copolymer incorporated into the matrix based on the weight of the ethylene / propylene copolymer.

6/7. DSC melting points for the polyethylene crystal fraction of ethylene / propylene copolymer (PE) and the polypropylene crystal fraction of the same copolymer are given in degrees Celsius. DSCΔH (heat of fusion) for PE and PP is given in calories per gram. The PE value represents the endothermic peak associated with the melting point of the polyethylene crystal fraction. The PP value represents the endothermic peak associated with the melting of the polypropylene crystal fraction. DSCΔH PE is the energy required to melt the polyethylene crystal fraction, and DSCΔH PP is the energy required to melt the polypropylene crystal fraction. These values are measured by ASTM D3147 and D3418.

8. Heat of fusion (ΔH total) is the heat of fusion due to ethylene crystallinity, measured by differential scanning calorimetry (DSC). This value is given as a percentage of the total heat of fusion. Polyethylene crystals melt at a temperature of 100 to 135 ° C. Polypropylene crystals, on the other hand, melt at a temperature of 150 to 170 ° C. The selected temperature of 140 ° C. is above the melting point of the ethylene / propylene copolymer but below the melting point of the polypropylene matrix. The heat of fusion ΔH of the ethylene / propylene copolymer is proportional to the polyethylene crystallinity, and the heat of fusion ΔH of the matrix is proportional to the melting point of the polypropylene crystal.

9. The diameter of the molded part is measured in inches.

10. Recovery rate represents the percentage change in diameter from the original diameter of the molded part to the current diameter of the molded part after age hardening for 24 hours. This percentage is based on the original diameter.

Claims (11)

Interpolymer of ethylene with at least one other alpha-olefin having a crystallinity of at least about 20% (a) at least 10% by weight (based on the weight of the total composition) of the homopolymer of propylene or propylene with at least one other alpha-olefin A method for producing a molded article, characterized in that the impact-resistant copolymer composition incorporated in the matrix of the polymer (b) is calcined at a temperature not lower than the melting point of the ethylene interpolymer or less than the melting point of the homopolymer or the interpolymer of propylene. The method of claim 1 wherein component (a) contains at least about 85% by weight of ethylene. The process of claim 1 wherein the crystallinity of component (a) is about 20 to about 60 weight percent. The method of claim 1 wherein component (a) is present in the impact resistant polypropylene copolymer in an amount of about 10 to about 50 weight percent, based on the weight of the impact resistant polypropylene copolymer. The process of claim 1 wherein one of the other alpha-olefins of component (a) is propylene. The method of claim 1 wherein the processing is at a temperature of about 130 to about 145 ° C. 3. The process of claim 1 wherein component (b) is a homopolymer of propylene. The process of claim 1 wherein component (b) is a copolymer of propylene and ethylene. A product produced by the process according to claim 1. (a) a crystallization degree incorporated in the matrix with (i) a matrix that is a homopolymer of propylene or a copolymer of propylene with at least about 5% by weight of one or more other alpha-olefins (based on the weight of the copolymer), and (ii) about 20% crystallinity A shock resistant polypropylene copolymer comprising at least about 10% by weight of copolymers of ethylene with at least one other alpha-olefin (based on the weight of the impact copolymer): (b) impact resistant polypropylene copolymer The plastic working process of the impact-resistant polypropylene copolymer characterized in that the plastic working at a temperature below the melting point of the component (ii) above the melting point. Product prepared by the method according to claim 10.